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Abstract:

In a method to execute a pause function in an inkjet printing system with
at least one printing apparatus, the pause function is triggered to
reduce a feed speed of the printing substrate web from a speed during
printing operation to a predetermined speed for a predetermined duration.
The duration is selected so that the printing substrate has suitable
properties with regard to at least one of the elements selected from the
group consisting of moisture and temperature under the printing unit of
the printing apparatus at an end of the pause function. After ending the
pause function, the printing substrate web is accelerated again to the
speed during the printing operation.

Claims:

1. A method to execute a pause function in a printing operation of an
inkjet printing system with at least one printing apparatus, comprising
the steps of: printing a printing substrate web with a printing unit with
print bars having print heads; triggering the pause function to reduce a
feed speed of the printing substrate web from a speed during the printing
operation to a predetermined speed for a predetermined duration, the
duration being selected so that the printing substrate web has suitable
properties with regard to at least one of the elements selected from the
group consisting of moisture and temperature under the printing unit of
the printing apparatus at an end of the pause function; and after ending
the pause function, accelerating the printing substrate web again to the
speed during the printing operation.

2. The method according to claim 1 in which suitable properties of the
printing substrate web are present when the printing substrate web has
adapted to environmental air with regard to moisture and temperature.

3. The method according to claim 1 in which, after triggering the pause
function at a lead time, the feed speed of the printing substrate web is
reduced to the predetermined speed, and said printing substrate web is
halted for the pause time period after expiration of the lead time.

4. The method according to claim 1 in which, after triggering the pause
function, the feed speed of the printing substrate web is reduced to the
predetermined speed for an entire pause time period.

5. The method according to claim 3 in which a feed of the printing
substrate web is measured by a rotary encoder wheel arranged before the
printing unit and a measurement result is supplied to a printer
controller, and wherein the lead time is selected so that a segment of
the printing substrate that is situated before the rotary encoder wheel
has arrived at the printing unit.

6. The method according to claim 3 in which first and second printing
apparatuses situated in series are used to print to the printing
substrate web, and in which the lead time is selected so that a segment
of the printing substrate web that is situated in the first printing
apparatus has arrived at a printing unit of the second printing
apparatus.

7. The method according to claim 4 in which first and second printing
apparatuses situated in series are used to print to the printing
substrate web, and after triggering the pause function, the feed speed of
the printing substrate web is reduced to the predetermined speed for the
entire pause time period.

8. The method according to claim 7 in which the printing unit of the
respective printing apparatus is moved away from the printing substrate
web after triggering the pause time period.

9. The method according to claim 6 in which a temperature of print heads
of a printing unit of the respective printing apparatus is reduced after
triggering the pause time period.

10. The method according to claim 6 in which the printing substrate web
is cooled between the first and the second printing apparatuses.

11. A method to execute a pause function in a printing operation of an
inkjet printing system with at least one printing apparatus, comprising
the steps of: printing a printing substrate web with a printing unit with
print bars having print heads; triggering the pause function to reduce a
feed speed of the printing substrate web from a speed during the printing
operation to a predetermined speed for a predetermined duration, the
duration being selected so that the printing substrate web has suitable
properties with regard to both moisture and temperature under the
printing unit of the printing apparatus at an end of the pause function;
and after ending the pause function, accelerating the printing substrate
web again to the speed during the printing operation.

Description:

BACKGROUND

[0001] Inkjet printing apparatuses can be used for single-color or
multicolor printing of a printing substrate, for example a belt-shaped
recording material made of the most varied materials (paper, for
example). The design of such inkjet printing apparatuses is known; see
for example EP 0 788 882 B1. Inkjet printing apparatuses that operate
according to the Drop on Demand (DoD) principle have a print head or
multiple print heads with nozzles comprising ink channels, the activators
of which nozzles--controlled by a print controller--excite ink droplets
in the direction of the printing substrate web, which droplets are
directed towards the printing substrate in order to apply print dots
there for a print image. The activators can generate ink droplets
thermally (bubble jet) or piezoelectrically.

[0002] Given printing of a printing substrate web, it is sometimes
necessary to stop the printing substrate web in a pause function during
the printing operation, for example in order to monitor the register
quality after printing a print job, or in order to correct problems in
the post-processing of the printing substrate web. After the resumption
of the printing substrate web, print image disruptions can then occur at
those web segments that were located directly under the print heads after
activation of the pause function. Due to the relatively large transfer
printing zone in inkjet printing apparatuses (inkjet printing systems,
for example), in particular in color printing, the print image
disruptions created due to the pause correspondingly cause a great deal
of maculature. The occurring print image defects contain print image
distortions, color register errors and trapezoidal print image
distortions. The causes for these are the swelling or shrinking of the
printing substrate web during the pause, and the position shifts of the
printing substrate web below the print heads that are linked with this.

[0003] These problems are explained using prior art FIG. 1. A printing
unit 1 and a printer controller 2 from a printing apparatus DR are shown.
The printing unit 1, which has print bars 4 with print heads 5 in series
(as viewed in the transport direction of the printing substrate web 3) is
arranged along a printing substrate web 3. In color printing, for
example, one print bar 4 is respectively provided per color to be
printed. The printing substrate web 3 is moved past the print bars 4 with
the aid of a discharge roller 9; it is thereby placed on a saddle with
guide rollers 8. Arranged at the input of the printing unit 1 is a rotary
encoder wheel 6 that is driven by the printing substrate web 3 and that
generates rotary encoder pulses depending on the feed motion of the
printing substrate web 3, which rotary encoder pulses are supplied to the
printer controller 2 and are used by the print controller 2 in order to
establish the point in time of the initiation of the print process at the
individual print heads 5. The printing substrate web 3 is supplied to the
rotary encoder wheel 6 by a drive roller 7 arranged before the rotary
encoder wheel 6.

[0004] In FIG. 1 it is now shown in principle how the printing substrate
web 3 can be affected in the individual web segments BA through the
printing apparatus DR by the printing unit 1 or the environmental air,
for example given a standstill of the printing apparatus DR. In the web
segment BA1 between drive roller 7 and rotary encoder wheel 6, the print
substrate web 3 is exposed to environmental air, with the consequence
that here a swelling of the print substrate web 3 can occur due to the
humidity of the environmental air. The change to the print substrate web
3 that is caused by this in the longitudinal direction is compensated
with the aid of the rotary encoder wheel 6, however. In the web segment
BA2 after the rotary encoder wheel 6 up to the printing unit 1, a
swelling of the print substrate web 3 due to the environmental air can
likewise occur which, however, remains unaccounted for by the rotary
encoder wheel 6. This also applies to the web segment BA3 under the print
heads 5 of the printing unit 1; there the print substrate web 3 can
shrink due to the operating temperature of the print heads 5; however the
printing substrate web 3 is also exposed to the environmental air, such
that the web segment BA3 can swell due to the moisture in the
environmental air, in particular given greater distances between the
print bars 4. The two influences overlap. The printing substrate web 3 is
thus exposed to different environmental influences from the drive roller
7 up to the discharge roller 9, which different environmental influences
can lead to a shrinking or to a swelling of the printing substrate web 3.
This can lead to the print image errors mentioned above, in particular if
the printing process is started again after a pause during the print
operation. [0005] Given triggering of the pause function, the following
effects on the printing substrate web 3 are thus to be considered:
[0006] Temperature and moisture difference between the print substrate
web 3 and the environmental air, with the swelling or shrinking of said
print substrate web 3 that are thereby incurred with this. [0007]
Temperature difference of the print heads 5 relative to the print
substrate web 3, with the shrinking of said print substrate web 3 that is
incurred with this.

SUMMARY

[0008] It is an object to specify a method in which the unwanted
influences of the temperature and the environmental air on the print
substrate web--and therefore on the print image--after triggering a pause
function are minimized, in particular after ending a print pause.

[0009] In a method to execute a pause function in an inkjet printing
system with at least one printing apparatus, the pause function is
triggered to reduce a feed speed of the printing substrate web from a
speed during printing operation to a predetermined speed for a
predetermined duration. The duration is selected so that the printing
substrate has suitable properties with regard to at least one of the
elements selected from the group consisting of moisture and temperature
under the printing unit of the printing apparatus at an end of the pause
function. After ending the pause function, the printing substrate web is
accelerated again to the speed during the printing operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a principle representation of a printing unit of an
inkjet printing apparatus;

[0011]FIG. 2 is a principle representation of a duplex printing system
with two printing apparatuses for printing to the front side and rear
side of a printing substrate web; and

[0012] FIGS. 3a-3c are diagrams that show the dependency of the feed speed
v of the printing substrate web on the time t in the various exemplary
embodiments of the pause function.

DESCRIPTION OF EXEMPLARY PREFERRED EMBODIMENTS

[0013] For the purposes of promoting an understanding of the principles of
the invention, reference will now be made to the preferred exemplary
embodiments/best mode illustrated in the drawings and specific language
will be used to describe the same. It will nevertheless be understood
that no limitation of the scope of the invention is thereby intended, and
such alterations and further modifications in the illustrated exemplary
embodiments and such further applications of the principles of the
invention as illustrated as would normally occur to one skilled in the
art to which the invention relates are included.

[0014] According to one exemplary embodiment, with triggering of the pause
function the feed speed of the printing substrate web is reduced from the
operating speed used in the print operation to a predetermined value for
a predetermined time period. The time period can be selected so that,
upon ending the pause, a printing substrate web with properties suitable
for printing (with regard to the moisture and/or temperature) is
presented under the printing unit of the printing apparatus; for example,
the printing substrate web has adapted to the environmental air with
regard to the moisture and the temperature.

[0015] After triggering the pause function, in a first exemplary
embodiment the feed speed of the printing substrate web can be reduced
from the operating speed to a predetermined speed for a predetermined
time period in a lead time upon printing, and after expiration of the
lead time period the printing substrate web can be stopped for a pause
time of 1 min (for example) in order to be able to subsequently
accelerate it to the operating speed again.

[0016] In a second exemplary embodiment, after triggering the pause
function the feed speed of the printing substrate web can be reduced from
the operating speed upon printing to a predetermined speed for the entire
pause time (of 1 min, for example) in order to be accelerated to the
operating speed again at the end of the pause.

[0017] The advantage of the method according to the exemplary embodiment
is that a web segment of the printing substrate web is situated under the
printing unit during the pause and after ending the pause, which printing
unit has values suitable for printing with regard to temperature and/or
moisture. These are values that the printing substrate web has when this
has adapted to the environmental air with regard to moisture and
temperature.

[0018] An exemplary embodiment is presented in FIG. 2 and with the
explanations of FIGS. 3a-3c.

[0019] Depending on the requirements of the print operation of an inkjet
printing apparatus, two different embodiments of the pause function
according to the exemplary embodiment are realized in the print jobs to
be processed or at the apparatuses for post-processing the printing
substrate web:

[0020] 1: Downtime pause with lead time

[0021] 2: Creep pause

[0022] Both pause variants lead to an improvement of the print quality by
reducing the aforementioned print image disruptions.

[0025] In the downtime pause with lead time, after operating a pause
button to interrupt the print operation the feed speed of the printing
substrate web 3 is reduced for a predetermined time period tv (FIG.
3b) from the operating speed vd to a speed vv before the
printing apparatus DR is stopped. For example, the feed speed of the
printing substrate web 3 can be reduced to vv=0.1 m/sec to 0.3 m/sec
for tv=1 to 3 min. The web segments BA2, BA1 are thereby adapted (in
terms of the temperature and humidity) to the environmental air and are
transported under the printing unit 1. At most, small, negligible
position fluctuations of the printing substrate web 3 then occur in the
following pause time tp. After ending the pause, segments of the
printing substrate web 3 that have suitable properties (with regard to
moisture or temperature) in the print operation are located under the
printing unit 1. The printing substrate web 3 is subsequently accelerated
again to the operating speed vd.

[0026] 2. Creep Pause

[0027] In the creep pause (FIG. 3c), upon operation of the pause button
the velocity of the printing substrate web 3 is reduced from the
operating speed vd to the creep velocity vs, for example to
vs=0.001 m/s to 0.015 m/s for the pause time tp. In this
variant of the pause function, a standstill of the printing substrate web
3 does not occur, such that new printing substrate web 3 is continuously
transported to the printing unit 1 and a shrinking of the printing
substrate web 3 due to a temperature difference or its expansion due to
moisture in the environmental air cannot have any effect since these
influencing factors also occur in the printing operation and have already
been compensated. A possibly arising slack of the printing substrate web
3 after the printing apparatus DR can then be taken up by the devices 13
(FIG. 2) for post-processing the printing substrate web 3.

[0028] II. Application of the Exemplary Embodiment in a Duplex Printing
System

[0029] 1. Explanation of the Special Problems in a Duplex Printing System

[0030] Special problems occur in the operation of a duplex printing
system. These problems and their solution are described using FIG. 2. A
printing system DS with two printing apparatuses DR1, DR2 (duplex
printer) is shown in principle in FIG. 2. Only the components of each
printing apparatus DR that are required to explain the preferred
exemplary embodiment are shown; the remaining components can be learned
from the prior art, just like the design of the individual components.
The printing unit 1 and a drying unit 10 of each printing apparatus DR
are shown in FIG. 2. Furthermore, a storage roller 11 of the printing
substrate web 3 is delivered from the printing substrate web 3 to the
first printing apparatus DR1, and a turning unit 12 and the rotary
encoder wheel 6 as shown between the printing apparatuses DR1, DR2. For
example, if the front side of the printing substrate web 3 is printed
with the printing apparatus DR1, the back side is printed with the
printing apparatus DR2. The printing substrate web 3 is turned by the
turning unit 12 between the printing apparatuses DR1, DR2. The feed of
the printing substrate web 3 is measured with the rotary encoder wheel 6,
and the measurement result is supplied to the print controller 2. A
rotary encoder wheel can also be provided at the input of the first
printing apparatus DR1. The print controller 2 receives the measurement
signals from the rotary encoder wheel 6 and controls the printing units 1
and the drying units 10 in a known manner. The printing substrate web 3
printed by the second printing apparatus DR2 is subsequently supplied to
the apparatuses 13 for post-processing.

[0031] If the pause function in such a duplex printer without application
of the exemplary embodiment is examined, the different causes for the
swelling or shrinking of the printing substrate web 3 in the printing
apparatuses DR1 and DR2 are to be considered:

[0032] Relationships in the first printing apparatus DR1:

[0033] For example, the print heads 5 of the printing unit 1.1 have an
operating temperature of approximately 32° C. The resulting
temperature difference from the temperature of the printing substrate web
3 leads to a shrinking of the printing substrate web 3 that is located
directly below the print heads. This shrinking of the printing substrate
web 3 and the movements of the printing substrate web 3 in the
longitudinal direction and in the transversal direction that are
connected with this cannot be registered by a rotary encoder wheel
arranged at the input of the printing unit 1.1. After ending the pause,
print quality defects therefore result at the first printing apparatus
DR1.

[0034] Relationships in the second printing apparatus DR2:

[0035] The printing substrate web 3 that has already been dried in the
drying unit 10.1 in the first printing apparatus DR1 after the printing
process takes up moisture from the environmental air during the pause,
which moisture leads to swelling of the printing substrate web 3. The
swelling of the printing substrate web 3 causes a length change of the
printing substrate web 3 in the longitudinal direction and transversal
direction both before and after the rotary encoder wheel 6. The swelling
of the printing substrate web 3 before the rotary encoder wheel 6, and
the web movement in the longitudinal direction that is connected with
this, are registered by the rotary encoder wheel 6 and communicated to
the printer controller 2, which accordingly corrects the point in time of
the activation of the print heads 5 of the printing unit 1.2. The
swelling of the printing substrate web 3 after the rotary encoder wheel
6, and the web movement connected with this (also that of the printing
substrate web 3 below the print heads of the printing unit 1.2), cannot
be registered by the rotary encoder wheel 6, which is why print pulses
corresponding to the movement of the printing substrate web 3 also cannot
be supplied to the print heads. This has an effect in the form of a print
image distortion. A shrinking of the printing substrate web 3 also occurs
below the print heads 5 of the second printing unit 1.2. However, here
the shrinking of the printing substrate web 3 counteracts the swelling of
the printing substrate web 3 due to the moisture of the environmental air
and thus reduces the print image errors resulting from this.

[0036] 2. Solution to the Problems in the Duplex Printing System that are
Illustrated Above

[0037] The measures of the preferred embodiment to avoid the effect of
these influences on the printing substrate web 3 (and therefore on the
print image) now have different effects in the two printing apparatuses
DR1, DR2 in a duplex printing system DS.

[0038] 2.1 Pause with Lead Time

[0039] a) Relationships in the Second Printing Apparatus DR2

[0040] During operation with reduced speed of the printing substrate web 3
during the pause lead time tv, the printing substrate web 3 is
provided with more time in order to acquire moisture via the
environmental air, such that the largest portion of the swelling of the
printing substrate web 3 has occurred with the standstill of the printing
substrate web 3 at the beginning of the pause. In order to bolster this
effect, additional measures can be taken that affect the take-up of the
moisture by the printing substrate web 3, insofar as the corresponding
means are provided at the printing apparatus DR: [0041] The printing
substrate web 3 can additionally be cooled with an existing cooling
device. [0042] The drying unit 10.1 for the printing substrate web 3 in
the printing apparatus DR1 can be deactivated. [0043] An air blower can
be arranged in the cross-turning region 12 before the second printing
apparatus DR2.

[0044] b) Relationships in the first printing apparatus DR1

[0045] Here measures can be taken via which the heating of the printing
substrate web 3 in the printing apparatus DR1 is reduced. If the pause
button is operated, the temperature of the print heads of the printing
unit 1.1 can be reduced (by 2-3° C.) during the pause lead time
tv, with the result that the printing substrate web 3 shrinks less
below the print heads.

[0046] Additional measures can be taken for both printing apparatuses DR1,
DR2: for example, in the printing operation the print heads can be moved
by up to 1 to 2 mm from the current print head position at the beginning
of the pause. A reduction of the heat transfer from the print heads 5 to
the printing substrate web 3 is thereby achieved.

[0047] 2.2 Creep Pause

[0048] During the creep pause, upon operation of the pause button the
speed of the printing substrate web 3 is only reduced, for example to
vs=0.001 m/s to 0.015 m/s. In this variant of the pause function, a
standstill of the printing substrate web 3 does not occur. A slack of the
printing substrate web 3 that possibly arises after the printing
apparatus DR2 must be taken up by the post-processing 13 of the printing
substrate web 3.

[0049] The printing unit 1 of a printing apparatus DR is shown in
principle in FIG. 1, for example that of the printing apparatus DR2
according to FIG. 2. A printing apparatus DR1 can be arranged before the
drive roller 7 as viewed in the transport direction of the printing
substrate web 3 (arrow PF). Contact with the environmental air can exist
both before and after the drive roller 7, with the consequence that the
printing substrate web 3 can swell. The degree of the swelling also
depends on the temperature of the printing substrate web 3 after leaving
the 1st printing apparatus DR1. Dimension changes of the printing
substrate web 3 before the rotary encoder wheel 6 are accounted for by
the rotary encoder wheel 6. However, dimension changes after the rotary
encoder wheel 6 can have a negative effect on the print image. If a pause
is now applied during the printing operation, for example to monitor the
register quality after printing a print job, the danger exists that the
printing substrate web 3 swells or shrinks before and below the second
printing unit 1.2, and the print heads 5 of the individual print bars 4
then no longer generate pinpoint print images on the printing substrate
web 3 upon resumption of the printing. In order to remedy this problem,
according to the exemplary embodiment either the lead time tv with
reduced feed speed vv of the printing substrate web 3 is inserted
before the pause, or the printing substrate web 3 moves with speed
vs in the creep during the pause. The consequence is that the
printing substrate web 3 can take up moisture from the environmental air,
and thus arrives below the respective printing unit in a state that also
exists during the print operation.

[0050] Diagrams of the speed v of the printing substrate web 3 plotted
over time t for the pause function of a printing apparatus DR result from
FIG. 3. [0051] The feed speed v of the printing substrate web 3
before, during and after the end of a pause in the printing operation
without application of the exemplary embodiment is shown in FIG. 3a. The
printing apparatus DR initially operates in the print operation; if the
printing substrate web 3 is transported through the printing apparatus DR
with the operating speed vd, the pause function is then initiated
and the printing apparatus DR is brought to a standstill (vp=0) for
a short time (of tp=1 min, for example). After the pause, the
printing substrate web 3 is started again and the printing substrate web
3 is accelerated to the operating speed vd again. [0052] The speed
curve of the printing substrate web 3 in the operation of the printing
apparatus DR in the pause function with lead is shown in FIG. 3b. The
printing substrate web 3 for the lead time tv (of 1 to 3 min, for
example) is braked from the operating speed vd to a low speed
vv of 0.1 m/s, for example. During this time, the printing substrate
web 3 can take on the moisture and temperature of the environmental air.
The printing substrate web 3 is subsequently halted (vp=0), for
example for a pause time tp=1 min. During this pause a problem in
the post-processing apparatuses can be corrected, for example. After
ending the pause, the printing substrate web 3 is accelerated again to
operating speed vd. [0053] The lead time tv can be selected so
that the printing substrate web 3 arrives under the printing unit 1, the
properties of which correspond in the printing operation and therefore
have already been taken into account. For example, the lead time tv
can also be selected so that the web segment BA1 (FIG. 1) arrives under
the printing unit 1; or, the lead time tv can also be selected so
that the printing substrate web 3 has arrived at the output of the first
printing apparatus DR1 or into the printing unit 1.2 of the second
printing apparatus DR2 after the drying unit 10.1. [0054] The pause
function with creep can be learned from FIG. 3c. After triggering the
pause function, the print speed of the printing substrate web 3 is
reduced from the operating speed vd to the creep speed of (for
example) vs=0.001 m/s and is transported further with this creep
speed vs during the pause (of tp=1 min, for example). After the
pause has expired, the printing substrate web 3 is accelerated again to
operating speed vd.

[0055] Although preferred exemplary embodiments are shown and described in
detail in the drawings and in the preceding specification, they should be
viewed as purely exemplary and not as limiting the invention. It is noted
that only preferred exemplary embodiments are shown and described, and
all variations and modifications that presently or in the future lie
within the protective scope of the invention should be protected.